1. Field of the Invention
This invention relates to an apparatus and method for applying a wrapped covering material around an elongate substrate or around a joint between such substrates, and in particular to an apparatus and method for applying tape or a wraparound sleeve around pipes or cables (or joints between pipes or between cables) in a void-free manner.
2. Introduction to the Invention
It is well known to wrap covering material around elongate substrates such as pipes or cables or joints therebetween in order to provide a protective coating, for example against corrosion or mechanical abuse or other environmental factors. One common example where a protective coating is required is where metal pipelines, factory coated with a thin polymeric outer layer (known as a mill coating), are joined by welding in the field. The mill coating is traditionally a sintered or extruded polyethylene layer. More recently multi-layer coatings comprising sequentially a fusion bonded epoxy layer, a hot melt adhesive layer and an outer polyethylene layer have become popular. Typical mill coatings are 1.5 to 9 mm thick. In order to form the weld, the mill coating, whatever its nature, must first be removed. This means that after the welding there is a bare pipe portion around the weld that needs to be protected. Solutions to this involve wrapping tape, e.g. polymeric tape, or a wraparound polymeric sleeve around the bare portion. Where a wraparound sleeve is used this may be heat recoverable (preferably heat shrinkable), and may be closed around the pipeline by an adhesive coated patch closure as described for example in U.S. Pat. No. 4,359,502, European Patent Publication No. 23,788, and European Patent Publication No. 163,508, and as also described, for example, in Raychem's WPC (Wraparound Pipe Sleeve) installation instructions. By a heat recoverable article is meant one whose dimensional configuration may be made to change when subjected to an appropriate treatment. Usually these articles recover, on heating, towards an original shape from which they have previously been deformed, but the term "heat recoverable" also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed. Typically heat-recoverable articles comprise a radially heat-shrinkable sleeve exhibiting the property of elastic or plastic memory, as described, for example, in U.S. Pat. No. 2,027,962, U.S. Pat. No. 3,086,242, and U.S. Pat. No. 3,597,372.
In order to achieve good bonding of the tape or sleeve to the pipeline it is known to preheat the substrate (in the case of an applied heat recoverable tape or sleeve) or to use epoxy primers applied to the pipeline before application of the sleeve or tape as described for example in European Patent Publication No. 181,233, the entire disclosure of which is incorporated herein by reference. Even with these additional precautions it is sometimes possible for air voids to be trapped between the covering sheet or tape and the underlying substrate, which may be undesirable in some circumstances. To remove or at least to minimize these voids it is known to use a hand-roller to roll out the voids in the heat-installed heat shrinkable sleeve or tape or in the cold-installed wrapped tape. Preheating of a substrate prior to installation of a heat-shrinkable sleeve, and hand-rolling of the shrunk sleeve, are both described, for example, in the above mentioned Raychem WPC installation instructions. While hand-rolling can be effective it is time consuming and, of course, installer sensitive.